1. Field
The present invention relates to a washing machine and a control method thereof, and, more particularly, to a washing machine that is capable of maintaining the balanced state of laundry to more smoothly perform a spin-drying operation and a control method thereof.
2. Description of the Related Art
Generally, a washing machine (normally, a drum-type washing machine) is a machine, including a water tub to receive water (wash water or rinse water), a cylindrical drum rotatably mounted in the water tub to receive laundry, and a motor to generate a drive force necessary to rotate the drum, that washes the laundry by lifting and dropping the laundry in the drum along the inner wall of the drum during the rotation of the drum.
The washing machine performs laundry cleaning through a washing operation of removing contaminants from laundry with water containing detergent dissolved therein (specifically, wash water), a rinsing operation of removing bubbles or remaining detergent from the laundry with water containing no detergent (specifically, rinse water), and a spin-drying operation of spin-drying the laundry at a high speed. For the spin-drying operation, as shown in FIG. 1, when a drum 10 is rotated at a high speed while laundry 12 is nonuniformly distributed along the inner wall of the drum 10, i.e., the laundry 12 is unbalanced, an eccentric force is applied to a rotary shaft of the drum 10, with the result that large vibration occurs.
In order to prevent the occurrence of the vibration due to the unbalanced state of the laundry, it is necessary to perform a process to uniformly distribute the laundry 12 in the drum 10, as shown in FIG. 2, before the spin-drying operation. This is because, when the spin-drying operation is performed in the unbalanced state of the laundry, the spin-drying time may be increased, and spin-drying errors may occur. In addition, when the laundry 12 is removed from the washing machine after the completion of the laundry cleaning, a large amount of force is required because the laundry is tangled, which causes dissatisfaction of main users.
In order to solve this problem, an unbalance reduction control procedure is performed to maintain the balanced state of the laundry 12 in the conventional art. As shown in FIG. 3, the unbalance reduction control procedure includes a laundry untangling process {circle around (1)} to untangle the tangled laundry 12 by rotating the drum 10 in alternating directions when a spin-drying operation is initiated, a laundry wrapping process {circle around (2)}-1 to attach the laundry 12 to an inner wall of the drum 10 by rotating the drum 10 at predetermined speeds rpm 1 and rpm 2, a laundry amount detecting process {circle around (3)} to estimate a weight of the laundry 12, an unbalance detecting process {circle around (4)} to estimate an unbalance size in the drum 10 using the estimated weight information and a control variable, such as a speed ripple or a current ripple, and a high-speed spin-drying process {circle around (5)} to discharge moisture contained in the laundry 12 outside using a centrifugal force caused by rotating the drum 10 at a high speed when the estimated unbalance size is within an allowable value. These processes are sequentially performed. When the estimated unbalance size is greater than the allowable value, on the other hand, the procedure returns to the laundry untangling process {circle around (1)} and then the unbalance reduction control procedure is repeated.
In the laundry wrapping process {circle around (2)}-1, the rotation speed is accelerated from the first rotation speed rpm1 to the second rotation speed rpm2, which is greater than a speed at which the laundry 12 sticks to the inner wall of the drum 10, and the state of the laundry 12 is not considered during the increase of the rotation speed of the drum 10 to the rpm2. For a load such as a small amount of laundry 12 or blue jeans, the balance of which is difficult to maintain, the unbalance is great, even after the laundry wrapping process {circle around (2)} is completed. As a result, it is not possible to rotate the drum 10 at a high speed, and the laundry untangling process {circle around (1)} may be reperformed. On the assumption that a probability of maintaining the balance through the laundry wrapping process {circle around (2)}-1 is 10%, and time required to perform the procedure from the laundry untangling process {circle around (1)} to the unbalance detecting process {circle around (4)} is 1 minute, for example, the balance is maintained after the unbalance reduction control procedure is performed 10 times on average, and therefore, it takes approximately 10 minutes until the high-speed spin-drying process is initiated. This spin-drying time is excessive.